Communications networks are used to transport a variety of signals such as voice, video, data and the like. As communications applications required greater bandwidth, communication networks switched to cables having optical fibers since they are capable of transmitting an extremely large amount of bandwidth compared with copper conductors. Fiber optic cables are also much smaller and lighter compared to copper cables having the same bandwidth capacity.
In certain applications, fiber optic cables are exposed to moisture that over time may enter the fiber optic cable. The moisture can migrate along the cable and enter cable splice enclosures, buildings, etc. To block water migration, fiber optic cables were provided with one or more components for blocking the migration of water along the fiber optic cable. By way of example, conventional fiber optic cables block water migration using a filling and/or a flooding material such as gel or grease within the fiber optic cable. Filling material refers to gel or grease that is inside a tube or cavity with the optical fibers, whereas flooding material refers to gel or grease within the cable that is outside of the cavity that houses the optical fibers. The gel or grease fills voids in the cable so that water does not have a path to follow in the fiber optic cable. Additionally, the gel or grease filling material provides cushioning and coupling of the optical fibers.
Gel or grease filling materials also have disadvantages. For example, the gel or grease may be messy and may drip from an end of the fiber optic cable. The filling material must also be cleaned from the optical fibers when being prepared for an optical connection, requiring the craft to carry cleaning materials into the field. Early fiber optic cable designs eliminated the flooding material by using cleaner, dry water-blocking components such as tapes or yarns outside the buffer tubes for inhibiting water migration. These dry water-blocking components typically include super absorbent polymers (SAPs) that absorb water and swell as a result, thereby blocking the water path for inhibiting the migration of water along the fiber optic cable. Generally speaking, the water-swellable components used a yarn or tape as a carrier for the SAP. Since the water-swellable yarns and tapes were first used outside the cavity housing the optical fibers, the other functions besides water-blocking such as coupling and optical attenuation did not need to be addressed.
Eventually, fiber optic cables incorporated water-swellable yarns, tapes, or super-absorbent polymers (SAPs) within the tubes that housed the optical fibers as a replacement for gel and grease filling materials. Generally speaking, the water-swellable yarns or tapes had sufficient water-blocking capabilities, but did not provide all of the functions of the gel or grease filling materials such as cushioning and coupling. For example, water-swellable tapes and yarns are bulky since they are relatively large compared with a typical optical fiber and/or can have a relatively rough surface. As a result, water-swellable yarns or tapes may cause problems if the optical fiber is pressed against the optical fibers. Likewise, the SAPs may cause problems if pressed against the optical fibers. In some cases, optical fibers pressed against conventional water-swellable yarns, tapes, and/or SAPs may experience microbending, which can cause undesirable levels of optical attenuation and/or cause other issues. Moreover, the desired level of coupling for the optical fibers with the tube may be an issue if the fiber optic cable is not a stranded design since the stranding provides coupling.
Other early fiber optic cable designs used tube assemblies that were highly-filled with SAPs in the form of loose powder for blocking the migration of water within the fiber optic cable. However, conventionally applied loose SAP powders within the fiber optic cable created problems since the superabsorbent powder particles, which were not attached to a carrier such as a yarn or tape, could migrate to and accumulate at positions within the fiber optic cable. When the cable was wound on a reel, such SAP powders could accumulate at the low points due to gravity and/or vibration, thereby causing inconsistent water blocking within the fiber optic cable. Also, loose SAP powders are free to fall out of the end of a tube.
FIGS. 15 and 16 respectively depict a transverse cross-sectional view and a longitudinal cross-sectional view of a conventional dry fiber optic assembly 10 having a plurality of optical fibers 1 along with schematically represented loose water-swellable powder particles 3 disposed within a tube 5. The conventional dry fiber optic assembly 10 uses a relatively large quantity of SAP powder 3 within tube 5 for blocking the migration of water therein. Other conventional fiber optic cable components have included embedded SAP powder in the outer circumferential surface of a tube, such as disclosed in U.S. Pat. No. 5,388,175. However, embedding the SAP in the outer surfaces of the tube greatly reduces the effectiveness of the powder since water may not reach the embedded particles.